Unless you use them for reference, or plan to read them again, why take up space storing books when you can pass them on to someone else in a kind of library without walls?

Ron Hornbaker believes they would be better off in the wild so others could read them.

Hornbaker is the founder of BookCrossing.com, an Internet book club that combines karma and kismet and encourages people to leave their books at coffee shops, parks, airports or anyplace else. Books are registered online, which allows members to follow where the books travel and who reads them.

As word spreads, membership has surged, turning the world into a sort of virtual library — with no late fees.

Lori Butler, a member from Upper St. Clair in suburban Pittsburgh, stumbled across the site while surfing the Internet and thought it would be a fun way to unload some of her books. She left her first stack on bleachers at the school pool where her children swim.

"I have tons and tons of books. It comes with being a teacher and librarian, I guess," said Butler, 34, a substitute teacher. "I just have too many to hold on to."

Butler, who goes by "pa-bookworm" on the site, leads Pennsylvania in releases with more than 200 books.

So far, though, just one person has responded. While that's been a bit disappointing, she said it's a worthwhile way of encouraging reading.

Rubyblue Black, 55, an American living in the Netherlands, finds the site addictive, as do others.

The site contains forums and allows people to track who has released the most books, the most popular books, most traveled books and more. Its addictive nature can carry a downside.

Black said she has neglected her house and garden, and her children and pets — members are compulsive readers. "If we're not reading books, we're reading the site. In time, someone will have to come with a support group for us," she said.

some 300 members join daily and the site registers more than 11 million page views a month, Hornbaker said. More than 34,000 members belonged in late August, with nearly 80,000 books registered.

Still, only about 15 to 20 percent of released books are registered as caught, but Hornbaker expects that to grow, pointing out that most members are new.

The site is a labor of love for Hornbaker and his software business, Humankind Systems. BookCrossing.com is free, but folks can buy items bearing the BookCrossing.com logo — a road sign showing a book crossing the street that Kaori designed — which helps defray costs.

"It carries itself on the strength of the idea," Hornbaker said. "It's something people have been doing all their life, we just sort of put technology behind it."